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Flexiforce Pressure Sensor - 100lbs.

Description: This is a piezoresistive force sensor from Tekscan. The harder you press, the lower the sensor’s resistance. Pressing hard, the resistance changes from infinite to ~300k. The sensor itself is thin and flexible, but the resistance does not change while being flexed. Resistance changes only when pressure is applied to the round area at the end of the sensor. Used as a presence sensor (someone standing), weight sensor, pressure sensor (impact testing), etc.

Hi, I have bought these Flexiforce sensors in order to create an insole that measure pressures points of the foot. The difficulty i am having is trying to calibrate the sensors. I have 500 g masses that I have been stacking on the the sensing area of the sensor, but I get very inconsistent voltage and resistance readings every time. Even the slightest movement to the masses creates a different reading for both voltage and resistance. Does anyone have any suggestions on how I can solve this problem?

Also, the force vs. resistance curve for the sensor shows that the resistance of the sensor drops to nearly 0 Kohms for a force above 1.3 lbs. However, I thought the sensor was still sensitive to up to 0-100 lb (according to the datasheet). Would anyone please let me know how I can detect the voltage/resistance change when different people stand on the insole if the change is resistance is not very noticeable? I will be placing the sensors on the toe, heel, first and fifth metatarsal point of the insole and need to then generate a pressure map showing the pressure points of the foot (in Matlab).

Are you able to convert the pressure or resistance into lbs.? For example if I had 4 sensors strategically embedded into pad which was then placed on a chair seat would I be able to estimate total weight of someone sitting on that pad?

Is it possible to bend this material? I would like to fasten this to the end of a metal object but the tip is only about .07 inches wide so I would have to bend the other end of this. Would that still be able to sense accurately?

Could someone offer some advise/guidance on hooking this up straight to an arduino (sans opamp)? Per the pdf datasheet, I have the top pin going to Analog 0 (the datasheet shows this pin going to an opamp, i believe). The middle pin is nothing. The bottom pin is “Vt -1v” which I tried hooking up to 5V and 5V with a resistor. I was getting analog sensor readings in the serial monitor, but they weren’t consistently correlated to pressure on the pad.

UPDATE: I figured it out. the “top pin” or left-side goes straight to 5V. The middle pin is nothing. THe right pin (or bottom pin) goes to Analog 0 (or any anolog pin you wish) but is also pulled low to ground with a resistor [I’m using a brown/black/green resistor which I believe is a 1mm ohm because it’s the only one I have for the moment and it works fine). No pressure yields a zero value. It’s very sensitive from 200-600. Hard pressure required to get above 600. Couldn’t very easily get to 1024 (the max). code is a simple analogRead on pin0.

You could gauge both air pressure and water pressure (to answer post above) by using a pressurized bladder inside a rigid vessel and measure the pressure of the bladder against the walls of the vessel. Not very precise though.

The sensors are vented so you wouldn’t be able to measure air pressure in this manner. You would need to completely cover the sensor with sealant as even the substrate is porous on a microscopic level. In any case, the sensors are intended for tactile forces, not air pressures, so you may not get the results you’re looking for.

I am curious if this could be used to detect water pressure. Could I build a sealed end-pipe fitting to put the senor part inside an irrigation system to detect water pressure? Do you have a sensor more suited for that purpose?
aeroponics101

From the user manual: “The length of the sensors can be trimmed by Tekscan to predefined lengths of 2?, 4? and 6? or can be trimmed by the customer. If the customer trims the sensor, a new connector must be attached. This can be accomplished by purchasing staked pin connectors and a crimping tool. A conductive epoxy can also be used to adhere small wires to each conductor.”

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